It accepts electron from NADH. These electrons are then passed down the chain. Proton will also be pumped out as NADH delivers electrons which will help contribute to the electron gradient needed to make ATP.
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It oxidizes NADH (producing NAD+ and H+) and it transfers those electrons to Ubiquinone (Coenzyme Q). It also actively transports 4 H+ from the matrix of the mitochondrion across the inner mitochondrial membrane.